Author Topic: Mustool G600 4.3 Inch LCD Microscope TFT display panel repair  (Read 470 times)

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Offline Johnny B Good

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Mustool G600 4.3 Inch LCD Microscope TFT display panel repair
« on: October 20, 2019, 12:20:22 am »
 Hello to all,

 I'm posting a request for help and/or advice on how best to repair one of these LCD microscopes (I now have two broken ones to play with :() Normally, I'd write off such broken on arrival kit and order from another supplier in the hope that the replacement won't suffer the same fate but such optimism now seems misplaced so I took a chance that a cheap colour TFT panel would get at least one of my broken G600s working again. Here's the whole tale of woe so far:-

 Having received not one but two of these LCD microscopes with broken TFT displays both almost identically broken with a cracked rear glass, the first after a 16 day wait on a Banggood delivery (quick by their standards) followed by an Ebay seller with UK stock after just an eight day wait, I decided to take a punt on buying a replacement panel from buydisplay.com after Banggood had refunded my purchase and gifted me the broken unit.

 The panel arrived in this morning's post. It was intact because unlike the microscopes, it had been properly packaged to give it a fighting chance of surviving the hazards of shipping. Unfortunately, all I can see after connecting it up to the Banggood unit is a blank but properly backlit screen (the LED backlight at least seems to be compatible with the LED driver used in the microscope at any rate).

 Since I had just been offered and had accepted a full refund on the second Ebay unit with no need to return the broken item just the night before, I was now fortuitously in a position to open up that second unit which, despite the cracked screen, did, unlike the Banggood unit, display a partial image proving that in this case, the problem was solely that of the damaged display (there had existed some small doubt as to whether the Banggood unit had suffered more than just a cracked LCD panel fault) to repeat my substitution test which, sadly for me, gave the same symptom.

 All of which means my replacement panel is either incompatible with the 'scope's interface despite the backlight working properly or else is faulty. Unfortunately, I have no other means by which to test it other than to get inventive with a signal generator to tickle the sync pulse lines in the 40 wire interface to see whether I can provoke some sort of reaction that might give me some hint of what's wrong.

 I suppose I could just play daft and report it as faulty so I can at least recover the 11 quid I'd spent in order to get hold of a fully functioning Mustool G600 LCD microscope (delivery of an intact unit via the usual means seems an almost improbable outcome to my mind in view of their alarming fragility in the face of the rigours of being shipped even just a couple of hundred miles across mainland Britain, let alone a 6000 miles plus journey from the PROC in a cargo glider towed from the stern rail of a container ship - 16 days of Banggood's "Priority Air Mail" after some 20 days of "Processing" :rant:).

 However, I was intrigued by the presence of four zero ohm 3 contact jumper links marked Jr1 to Jr4 on the flexi-pcb which suggests the possibility that it may simply be misconfigured for my intended use, leaving a faint hope that it might just be a case of rejigging these 0 ohm resistor links to make it compatible with the G600's display interface settings. I know this is "clutching at straws" but it does beg the question which I ask of anyone with experience of these displays as to whether there is any basis for this hope of a 'quick fix'?

 The TFT panel I'd purchased from buydisplay.com was the ER-TFT043-3 model. It had the same 40 wire flexi-pcb ribbon connector as the one used in the microscope and another, seemingly identical unit I'd checked out on AliExpress here:

https://www.aliexpress.com/item/32949158074.html?spm=2114.search0306.3.112.365a3cabWFyb1s&ws_ab_test=searchweb0_0,searchweb201602_0,searchweb201603_0,ppcSwitch_0&algo_pvid=8e1ff942-b08a-4751-8c29-c1d69f3ed000&algo_expid=8e1ff942-b08a-4751-8c29-c1d69f3ed000-16

 or one very similar (and just about every other 4.3 inch 480 by 272 colour TFT with or without a touch screen sensor - I didn't need a touch screen sensor for this job).

 At the time, I wasn't too keen on selling my soul to yet another data miner so elected to buy from buydisplay.com via the services of ebay for just literally a few pennies more and no more delivery delay than I was being promised by AliExpress who no doubt base their delivery promises on the Banggood model. Let's just say I felt much less discomfort using the (tried and tested) Ebay route to 'happiness'.

 The only niggle I had over the buydisplay.com panel was the plethora of smd parts attached to the flexi-pcb versus none whatsoever on the original and the AliExpress part I'd seen 'pictured' (pictures on Chinese Sellers' web shops are about as trustworthy as a nine bob note) but I thought, "It's a "common display" with the universal 40 wire flexi-pcb ribbon that the whole world and their dog have chosen as a de-facto standard for a 24bit parallel RGB interface on each and every one of these 4.3 inch colour TFT display panels (even the Kathode and Anode LED backlight connections are all in the same place, pins 1 and 2) so, Just how hard can it be?" :-\

 Perhaps I should have played safe and chosen that AliExpress unit which looked a dead ringer for the ones used in the G600 microscope (assuming the pictures could be trusted)? Here again, I'm hoping to attract the attention of anyone with any sort of display technology experience who might be able to offer some advice or helpful hints. With this in mind, I've attached a few photos of the original display panel to show the part number and the flexi-pcb ribbon cable.

[EDIT 20191020 15:07]

 I've been doing some more 'research' (learning far more than I really aught to know about colour TFT panels - in particular, interfacing) and came across this useful source:

https://tinyurl.com/y5onm57f

 which clearly demonstrates that I am in fact dealing with an RGB interfaced TFT replacement panel. Every single picture with this classic 40 way flexi-pcb ribbon connector lists only the RGB interface option, all others, sans such flexi-pcb connector being either SPI/UART (always that combo-never an either/or option) or MCU. Whatever lingering doubts I had before embarking on this "Holy Grail" like quest are now well and truly set aside. This conclusion is further reinforced by the following quote I found here: https://www.lcd-module.com/produkte/grafik.html which says:-

"TFT Panel - Same Connector for all !
Who is not already desperate at the different pin assignments and connector types with different TFT displays? This is now the end. All TFT displays from our company have an identical connection with 40 pins in a grid of 0.5mm. Also the pin assignment itself is almost identical. A matching ZIFF connector is available as an accessory."

 That of course, is not to say that there may well be other pitfalls despite the apparent use of an industry standard 40 pin TFT panel RGB interface (see below).

 By restricting my choice to RGB types with the default controller option set, I've been able to look at two examples of screens without touch controller and one with a capacitive touch controller where pin 31 (Display on/off) is used to reverse the normal negative VSYNC polarity to positive when pulled low. Presumably with no connection from the driving device, this is pulled up, making the VSYNC behave normally.

 I had initially thought that this might be a possible cause of the lack of an image with the replacement display but, even if such a display is used in place of one where this pin 31 signal is used as a normal enable/disable to turn the display on and off, the end effect where it's used to reverse the VSYNC polarity should be virtually the same.

 Of course, if Mustool have gone out of their way to frustrate a basic DIY repair attempt to replace their booby trapped displays which seem to be almost guaranteed never to survive shipping by specifying such a display type in order to use a contrary positive going VSYNC signal, then it will foil attempts to use the more common TFT display type unless the canny DIY repairer adds an inverter to this control line or finds the hidden polarity reversing option jumper (most likely a solder blobbed pad pair or a low value smd resistor placement so as to avoid the "Burning your Bridges" effect should Mustool's cheap supply of quirky display panels ever dry up).

 With all of the above discoveries, it would seem my faith in assuming I'd have every chance of success with that buydisplay purchase was not entirely unjustified. However, either the replacement panel is faulty or else Mustool have incorporated some form of incompatibility into their design to hold onto the business of expensive repair work. All I'm attempting to do right now is to "Leave no stone unturned" before giving up and returning the buydisplay panel as faulty for a refund.

JBG
« Last Edit: October 20, 2019, 06:17:43 pm by Johnny B Good »
John
 

Offline Johnny B Good

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Re: Mustool G600 4.3 Inch LCD Microscope TFT display panel repair
« Reply #1 on: October 27, 2019, 03:40:17 am »
 By way of closure to this thread, I'm reporting the final outcome of my failed attempt to repair the Mustool G600 LCD microscope using a standard 40 wire parallel RGB interfaced 4.3 inch colour TFT display sourced from buydisplay. I'm a little bit disappointed and very surprised at the lack of any response but I guess I must be the only one daft enough to attempt such a repair on a product manufactured by the inscrutable Chinese with no datasheets whatsoever to guide me.

 Once more I 've ASS U ME d more than I should have and landed up wasting money on a futile repair attempt. Still, that's the problem with being the optimist that I am. Anyway, for what it's worth, here's what happened.

 I just received a 40Pin 0.5mm FFC FPC to 40P DIP 2.54mm PCB Converter Board Adapter (break out board) yesterday morning (Saturday) which, after soldering two 20 pin headers, cranked to a 0.3 inch spacing to plug into a breadboard, allowed me to buzz out the connections to identify the three ground pins (3,29 and 36) and the Vcc/Vdd on pin 4 and all the input pins on both broken Mustool displays and the replacement buydisplay sourced panel.

 They all matched except for the group of pins normally assigned as Green and Blue data bits 0-7 in the Mustool 40 wire interface which were all open circuit (NC). The buydisplay panel tested exactly as per its datasheet would lead me to expect with such a basic continuity/resistance to ground pin test.

 With only the R0-R7 pins connected to inputs in the Mustool display's 40 wire interface, I'm tempted to believe the RGB signals are multiplexed via pins 5 to 12 inclusive (else why so many input lines?). However, despite searching for data sheets regarding displays that use this form of multiplexed RGB parallel interface, I haven't been able to confirm that such an 8 bit multiplexed parallel RGB interface works as I suppose.

 However, I have seen references in tft display on-glass controller chip data sheets to the use of a 20MHz dot clock (versus the more usual 9MHz one with the non-multiplexed parallel RGB interfaces) which could allow such multiplexing to still support a respectable 40fps refresh rate so I may actually be correct in this assumption (it's hard to decipher such on-glass display chip data sheets). Regardless of the exact details, it's quite clear that Mustool have used an interface that doesn't match the parallel RGB one commonly seen with the ubiquitous 40 wire TFT display panels so it looks like I owe buydisplay an apology for assuming they'd supplied me with a faulty display panel. :-[

 I had two examples of broken Mustool display panels to test with so I'm quite certain that the damage to the rear glass panel is not the cause for pins 13 to 28 all testing as N/C whilst all the rest tested as expected, including matching that of the buydisplay panel.

 If I'm correct about the RGB ttl level (3.3v) parallel signals being multiplexed at a 20MHz dot clock rate, then it would neatly explain why the buydisplay panel failed to respond to whatever data was being presented on the Red data lines since its dot clock is only rated for slightly faster than 9MHz and would not have responded to such a fast clock rate.

 There might be a jumper or two on the Mustool camera control board to change it from the bastard 8 bit multiplexed parallel RGB mode to the more standard 24 bit format (RGB565, RGB666 or RGB888 modes) but since it was a case of "Third time lucky" with my third purchase of a Mustool G600 from a second Ebay trader shipping from a UK warehouse, I no longer see any immediate need to delve any further into the mysteries of this microscope.

 One fully functioning (after a minor mix and match of rear and front halves with the other ebay unit because the third unit was missing the blue smd LED on its camera board) is all I need. Assuming return postage doesn't kill the deal, I'm better off returning the buydisplay panel for a refund on an item that would otherwise just sit in my parts bin unused.

 For anyone who may be attempting a similar exercise but has managed to find this thread before optimistically ordering a "Common 40 wire" TFT display panel, the news isn't good. The Mustool display panel doesn't conform to this common standard so don't waste your time and money on a 'standard' panel. It looks like it's a panel that's multiplexing the RGB data over pins normally assigned to the red channel in an otherwise standard 40 wire interface (ICBW and it might be something else again but why use up 8 input lines if that is the case?).

 Unless you're already familiar with all the varied options possible with such 40 wire interfaced display panels, you have a lot more testing and research ahead of you to avoid the trap of thinking, "It's a 40 wire interfaced display, just how hard can it be?" and landing up with an incompatible replacement panel as I did. Obviously, if anyone does manage to track down a compatible display panel, a follow up post to this thread won't go to waste. I might have lost interest but I'm sure there'll be others who might better appreciate the additional information.

JBG
John
 

Offline Johnny B Good

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Re: Mustool G600 4.3 Inch LCD Microscope TFT display panel repair
« Reply #2 on: November 20, 2019, 12:32:15 pm »
 After 14 days with no news of the returned (at my own cost) display panel, I finally received emails from Ebay and Paypal today, confirming that buydisplay had received my return and issued its original dollar cost of $13.76 by way of a refund which Paypal had converted into a £10.61 credit to my debit card which was just £1.03 short of the original pounds Sterling I'd been charged.

 I'd expected such a currency exchange loss but once you have started a returns process with ebay, you can no longer view the original transaction details in regard of what you'd been charged in pounds Sterling at the time, just the Dollars US price and this particular transaction had somehow failed to show up in my internet banking's weekly summary reports which would normally show these transactions so I'd had to resort to the messy and convoluted business of logging into my bank's internet banking system before I could finally track down this particular transaction to verify just how much more than the return postage costs I'd had to endure in minimising the cost of my mistake in ordering an incompatible replacement display panel in the first place.

 The Lord Murphy moves in mysterious ways that go beyond His infamous party trick of teleporting SMD components into an alternative dimension whenever they get pinged off a work bench towards a floor possessed of any 'ground clutter' (carpet pile, or any layer of general detritus or WHY). Little wonder then that humanity has been in the habit of creating religions out of such otherwise inexplicable events which range from random lightning bolts striking dead both friend and foe alike to the phenomena that toast almost always falls butter side down onto the floor, seemingly in defiance of all the odds normally associated with such 'coin toss' outcomes.

 It may seem a bit of a leap to equate my experience with such philosophical musings on the propensity of mankind to invent religions but when what should have been a straightforward process of assessing the financial damage of my mistake becomes bogged down with such unexpected obstacles, it's hard to avoid taking note of it as yet another example of "Murphy's Law" in action which is the obvious base for Mankind's need to invent "Gods" and religions by which to appease such mystical beings in the hope of a better life, whether this or the next.

 Anyhow, philosophical musings aside, I did actually obtain a refund to mitigate the expense of my misguided attempt at repairing one of those two broken G600 microscopes I'd been afflicted with and I can now stop fretting about being stuck with a part I'm unlikely to ever find any use for. In the circumstances, the result was about as good as I could hope for (a salutary lesson at a minimised cost). ::)

JBG
John
 


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